1. Field of the Invention
The present invention relates to the field of medical devices. More specifically, the present invention relates to cardiac pacemakers and assemblies containing them for use in epicardial implantation.
2. Description of Related Art
Complete heart block in the fetus is a life-threatening emergency with no effective treatment options beyond watchful waiting. Fetal bradycardia due to heart block can be persistent in utero, and hydrops fetalis can develop in more than a quarter of these pregnancies. Once hydrops fetalis occurs, if the fetus cannot be delivered due to prematurity or other clinical concerns, fetal demise is nearly inevitable.
Due to the often severe consequences of fetal heart block, various treatment options have been undertaken in an effort to treat these fetuses. Pharmacologic therapy has been trialed, usually with administration of medications to the mother with anticipated placental passage of the agent to the fetus. Because damage to the fetal cardiac conduction system is believed to be due to maternal autoimmune antibodies in many of these cases, fluorinated steroids have been used to prevent or reverse the heart block. Studies on this therapy, however, have demonstrated unclear, if any, benefit from these agents. Intravenous gammaglobulin has also been administered to these patients in an attempt to reverse or halt progression of the immunologic damage, but results of this therapy have also been disappointing. Beta-adrenergic agents are known to increase heart rates in children and adults, but maternal administration of these agents results in heart rate increases that have not been proven to affect overall survival.
When a newborn, child, or adult presents with symptomatic complete heart block, treatment usually consists of implantation of a pacemaker to ensure an adequate heart rate. With appropriate pacing, these patients are usually asymptomatic with an excellent prognosis. Similar benefits would be expected from pacing a fetus with complete heart block, theoretically allowing resolution of hydrops in 1-2 weeks and permitting an otherwise normal gestation. A conventional pacemaker would then be implanted at delivery. Over the last two decades, several investigators have attempted to place pacemakers in a fetus. To date, however, there have been no survivors of fetal pacing. Previous approaches have relied on the placement of a pacing wire on the fetal heart with an extra-uterine pulse generator implanted in the mother. This has inevitably failed because of lead dislodgement due to fetal movement.
U.S. patent application publication number 2012/0078267, which is incorporated herein by reference, discloses a pacemaker device and device assembly. The pacemaker device is disclosed as having an electrode for connecting the device to fetal heart tissue. The electrode is attached to a relatively short wire or lead that connects the electrode to a power source located on the proximal end of the device. The pacemaker device further comprises a coil retention mechanism that retains the lead within a recess in the body of the pacemaker device until the pacemaker device is deployed in a patient. The coil retention mechanism is held in contact with the body of the pacemaker device by a “holder”, which can be a string, thin wire, or elastic band that runs along the sides and across the distal end of the pacemaker device. The pacemaker device can be provided as part of a device assembly, which includes the pacemaker device and a “pusher”, which is in essence a rod or rod-like element that can be used to implant and deploy the pacemaker device into cardiac tissue. The pusher is held in contact with the pacemaker device by the holder. In use, the pacemaker device is implanted into cardiac tissue through force applied on the pusher (e.g., by rotating the pusher about its central axis to impart a twisting motion to a screw-like electrode, resulting in implantation of the electrode into cardiac tissue). Once the pacemaker is implanted, the holder is cut and removed, thus allowing the lead to extend from the pacemaker device body, and the pusher to be removed from the pacemaker device. While the device and device assembly represent a significant advancement in the art, and in particular for treatment of fetuses, improved technologies would advance the pacemaker art.